Supporting ZeroMQ

[saul-jb]

ZeroMQ imposes specific framing on a transport and therefore requires further detail added to the address to differentiate it from a standard transport. For example: /ip4/127.0.0.1/tcp/3000 describes how to reach a server but if that server is running a 0MQ socket on it, standard tcp applications will not be able to communicate therefore an extension will be needed to adequately describe it: /ip4/127.0.0.1/tcp/3000/0mq

There are a lot of protocols (like #106) that require additional information added to the address, perhaps a multiaddr code that describes a generic protocol could be useful. For example: /ip4/127.0.0.1/tcp/3000/protocol/0mq This would allow developers to use multiaddr without requiring custom additions directly to the table. However this would only solve protocols that don't require a value since the protocol name becomes that value part - I think #70 might be more along the lines of that.